For 8.0 servers, get last built-in oid from pg_database

We didn't start ensuring that all built-in objects had OIDs less than
16384 until 8.1, so for 8.0 servers we still need to query the value out
of pg_database.  We need this, in particular, to distinguish which casts
were built-in and which were user-defined.

For HEAD, we only worry about going back to 8.0, for the back-branches,
we also ensure that 7.0-7.4 work.

Discussion: https://www.postgresql.org/message-id/flat/20160504183952.GE10850%40tamriel.snowman.net

src/bin/pg_dump/pg_dump.c

@@ -96,6 +96,12 @@ bool		g_verbose;			/* User wants verbose narration of our
 /* subquery used to convert user ID (eg, datdba) to user name */
 static const char *username_subquery;
 
+/*
+ * For 8.0 and earlier servers, pulled from pg_database, for 8.1+ we use
+ * FirstNormalObjectId - 1.
+ */
+static Oid g_last_builtin_oid; /* value of the last builtin oid */
+
 /* The specified names/patterns should to match at least one entity */
 static int	strict_names = 0;
 
@@ -233,6 +239,7 @@ static char *convertRegProcReference(Archive *fout,
 						const char *proc);
 static char *convertOperatorReference(Archive *fout, const char *opr);
 static char *convertTSFunction(Archive *fout, Oid funcOid);
+static Oid findLastBuiltinOid_V71(Archive *fout, const char *);
 static void selectSourceSchema(Archive *fout, const char *schemaName);
 static char *getFormattedTypeName(Archive *fout, Oid oid, OidOptions opts);
 static void getBlobs(Archive *fout);
@@ -684,6 +691,20 @@ main(int argc, char **argv)
 		exit_horribly(NULL,
 		   "Exported snapshots are not supported by this server version.\n");
 
+	/*
+	 * Find the last built-in OID, if needed (prior to 8.1)
+	 *
+	 * With 8.1 and above, we can just use FirstNormalObjectId - 1.
+	 */
+	if (fout->remoteVersion < 80100)
+		g_last_builtin_oid = findLastBuiltinOid_V71(fout,
+													PQdb(GetConnection(fout)));
+	else
+		g_last_builtin_oid = FirstNormalObjectId - 1;
+
+	if (g_verbose)
+		write_msg(NULL, "last built-in OID is %u\n", g_last_builtin_oid);
+
 	/* Expand schema selection patterns into OID lists */
 	if (schema_include_patterns.head != NULL)
 	{
@@ -1494,7 +1515,7 @@ selectDumpableCast(CastInfo *cast, Archive *fout)
 	 * This would be DUMP_COMPONENT_ACL for from-initdb casts, but they do not
 	 * support ACLs currently.
 	 */
-	if (cast->dobj.catId.oid < (Oid) FirstNormalObjectId)
+	if (cast->dobj.catId.oid <= (Oid) g_last_builtin_oid)
 		cast->dobj.dump = DUMP_COMPONENT_NONE;
 	else
 		cast->dobj.dump = fout->dopt->include_everything ?
@@ -1526,7 +1547,7 @@ selectDumpableProcLang(ProcLangInfo *plang, Archive *fout)
 		plang->dobj.dump = DUMP_COMPONENT_NONE;
 	else
 	{
-		if (plang->dobj.catId.oid < (Oid) FirstNormalObjectId)
+		if (plang->dobj.catId.oid <= (Oid) g_last_builtin_oid)
 			plang->dobj.dump = fout->remoteVersion < 90600 ?
 				DUMP_COMPONENT_NONE : DUMP_COMPONENT_ACL;
 		else
@@ -1552,7 +1573,7 @@ selectDumpableAccessMethod(AccessMethodInfo *method, Archive *fout)
 	 * This would be DUMP_COMPONENT_ACL for from-initdb access methods, but
 	 * they do not support ACLs currently.
 	 */
-	if (method->dobj.catId.oid < (Oid) FirstNormalObjectId)
+	if (method->dobj.catId.oid <= (Oid) g_last_builtin_oid)
 		method->dobj.dump = DUMP_COMPONENT_NONE;
 	else
 		method->dobj.dump = fout->dopt->include_everything ?
@@ -1577,7 +1598,7 @@ selectDumpableExtension(ExtensionInfo *extinfo, DumpOptions *dopt)
 	 * change permissions on those objects, if they wish to, and have those
 	 * changes preserved.
 	 */
-	if (dopt->binary_upgrade && extinfo->dobj.catId.oid < (Oid) FirstNormalObjectId)
+	if (dopt->binary_upgrade && extinfo->dobj.catId.oid <= (Oid) g_last_builtin_oid)
 		extinfo->dobj.dump = extinfo->dobj.dump_contains = DUMP_COMPONENT_ACL;
 	else
 		extinfo->dobj.dump = extinfo->dobj.dump_contains =
@@ -8820,8 +8841,8 @@ dumpExtension(Archive *fout, ExtensionInfo *extinfo)
 		/*
 		 * We unconditionally create the extension, so we must drop it if it
 		 * exists.  This could happen if the user deleted 'plpgsql' and then
-		 * readded it, causing its oid to be greater than FirstNormalObjectId.
-		 * The FirstNormalObjectId test was kept to avoid repeatedly dropping
+		 * readded it, causing its oid to be greater than g_last_builtin_oid.
+		 * The g_last_builtin_oid test was kept to avoid repeatedly dropping
 		 * and recreating extensions like 'plpgsql'.
 		 */
 		appendPQExpBuffer(q, "DROP EXTENSION IF EXISTS %s;\n", qextname);
@@ -15324,6 +15345,33 @@ dumpTableConstraintComment(Archive *fout, ConstraintInfo *coninfo)
 	destroyPQExpBuffer(labelq);
 }
 
+/*
+ * findLastBuiltinOid_V71 -
+ *
+ * find the last built in oid
+ *
+ * For 7.1 through 8.0, we do this by retrieving datlastsysoid from the
+ * pg_database entry for the current database.
+ */
+static Oid
+findLastBuiltinOid_V71(Archive *fout, const char *dbname)
+{
+	PGresult   *res;
+	Oid         last_oid;
+	PQExpBuffer query = createPQExpBuffer();
+
+	resetPQExpBuffer(query);
+	appendPQExpBufferStr(query, "SELECT datlastsysoid from pg_database where datname = ");
+	appendStringLiteralAH(query, dbname, fout);
+
+	res = ExecuteSqlQueryForSingleRow(fout, query->data);
+	last_oid = atooid(PQgetvalue(res, 0, PQfnumber(res, "datlastsysoid")));
+	PQclear(res);
+	destroyPQExpBuffer(query);
+
+	return last_oid;
+}
+
 /*
  * dumpSequence
  *	  write the declaration (not data) of one user-defined sequence